The ability of aircraft to travel at supersonic velocities puts great demands on the aircraft's propulsion system. Travel at supersonic velocities means an increase in weight of both airplane and fuel at take off and becomes an exponential increase in the power required, particularly at zero velocities. To meet such unprecedented demands for lift and thrust propulsion, different types and categories of engines and engine cycles used separately or in tandem have been proposed and some have been referred to as combined-cycle engines.
A great amount of power can be made available if an oxidizer is chemically or physically combined with the fuel, or otherwise carried separately, as is the case with rockets. But this must be done judiciously because oxygen weighs many times more than hydrogen and can lead to mixtures that are very fast acting and explosive. This added weight must be overcome, adding inertial liabilities to the operational proficiencies, particularly from zero velocity start up through low speed takeoff procedures. Exponentially larger fuel and oxidant requirements are required over propulsion systems that acquire oxygen from the ambient air and do not have to carry the added weight of the oxidizers as well as carrying the heavy containment tanks. Further, the impulse velocity resonance of the rocket combustor is limited by the physical constraints of dimension parameters and efficiency losses at low speed operation. Impulse resonance reaction times and burning rates measured in thousands of a second are produced within the combustion reaction cones while achieving exhaust velocities that may reach 21,000 feet per second relative to the rocket at all operational speeds with correspondingly high operating temperatures. This allows such rockets to realize concomitant equal and opposite reaction response, accumulating very high maximum escape velocities providing they reach the frictionless expansions of space quickly, which they can do. Mandating very abrupt times to reach optimum altitude and velocity causes the rockets to expend all their vast fuel and oxidant reactants in the range of four minutes, more or less. Liquid reactant rockets are complex and expensive and predisposed to malfunction.
Solid propellant rockets, although very simple, are made up of reactants that are usually toxic and polluting and not prone to easy restarting. All aspects of rocketry must be considered before deciding to integrate their propulsive drive into hybrid interaction with the driving potential of Ram or Scramjet air-breathing engines. There are more versatile, efficient, high performance alternatives available that utilize less overtly explosive hypergolic reactants, which are prone to be expensive, tricky to use (sensitive and temperamental), dangerous, poisonous, highly polluting and a very wasteful means of lifting weights into space or near space upper altitudes being loaded down as they are with onboard oxidants.
Conventional by-pass turbojet engines with afterburners can be made to function as a “combined-cycle” engine if part of the intake air is shunted around the core by-pass turbojet engine and directed into the afterburner. Then once having obtained transition velocity, the engine is run as a Ramjet engine by shutting down or shutting off the core by-pass turbojet engine. The by-pass turbojet engine may be run acting to supercharge the Ramjet conformation variation. It is not hard to visualize the two aspects of both engine functions being run simultaneously. The ramjet bypass conforming aspect of the engine can be run relatively independent of the core by-pass turbojet engine, and it is this characteristic of the engine design that has become referred to as a combined-cycle turbojet engine. Such an arrangement is shown in FIG. 11, which is reproduced from Edelman, U.S. Patent Pub. No. 2005/0081508 A1, published on Apr. 21, 2005. In FIG. 11, element 111 indicates the combustion chamber vessels and arrangements.